JPS646609B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention relates to digital distance relays.

<Prior Art> Distance relays have been digitally realized for some time, and one example is a relay in which the main part is configured as shown in FIG. 3a. Figure 1 shows the characteristics of the directional element (also called the Moh element) of such a distance relay. In the figure, the inside of the circle is the operating range, Zs is the setting impedance value,
V and I respectively indicate the voltage and current values taken in from the system to be protected. The directional element operates when the storage voltage is Vm and the condition (ZsI-V)·Vm≧0 is satisfied.

In FIG. 3a, the voltage and current of the system are sampled at regular intervals and then digitized by an analog-to-digital converter and provided as inputs V and I. The prefilter 21 is the product of FIG.
Provided to obtain ZsI. Then, the value of ZsI-V is calculated from this output and the taken input V in the synthesis section 23, and the storage section 24 stores this value and the voltage for several cycles in order to operate normally in the event of an internal close end fault. The product calculation unit 25 calculates the product of the output Vm and the output Vm. This product output becomes a DC component and a second harmonic component when the input information is only the fundamental wave, so it is divided into a DC component and a second harmonic component.
A post-filter 22 is provided to integrate and remove the second harmonic component. Therefore, the output of the post-filter 22 is as follows: where V _M and I _M are the amplitudes of V and I,
And when Z=V _M /I _M , and the phase angle between ZsI and I is φ, and the phase angle between V and I is θ, then 1/2 {I ² _M Z・Zs cos (φ − θ) − I ² _M・Z ² }. Therefore, if an accident is determined using the formula I ² _M Z・Zs cos (φ−θ)−I ² _M Z ² >0, the digital distance with a phase characteristic such as Z<Zs cos (φ−θ) A relay is obtained. Further, a specific example of the configuration of the storage unit 24 is shown in FIG. 3b.
Shown below. According to this example, an appropriate gain difference and delay time difference are provided between the first arithmetic processing section 27 and the second arithmetic processing section 28, and the combining section 26
The output of 8 and the input signal V are combined, and this is passed through the first arithmetic processing section 27 and used as one input of the product calculation section 25.

<Problems to be Solved by the Invention> The above-mentioned conventional digital distance relay has a product calculation section 25 in its main part, and is a method for calculating the product of vector quantities synthesized by input signals V and I. , a post-filter is required to remove the second harmonic component included in the product output. For this reason, the configuration of the relay becomes complicated, and if the input signals V and I are accompanied by distortion, and the selectivity (steepness) of the post-filter is low, the error of the relay becomes large. In order to eliminate this problem, the selectivity of the filter must be increased, making it difficult to adjust the filter and causing unstable response.

In addition, depending on the values of the gains and delay times of the first and second arithmetic processing units 27 and 28 in the memory unit 24, an unreasonable memory voltage may be output for the memory operation of the relay. There are also points.

This invention was made in view of the above-mentioned problems, and an object thereof is to provide a digital distance relay that does not require a post-filter and that can obtain a very reasonable storage voltage for the storage operation of the relay. do.

<Means for Solving the Problems> The present invention solves the above problems by the following means. That is, the system voltage and current are sampled, digitized, and stored in a memory circuit over l cycles (l is an integer of 1 or more). A calculation circuit for calculating the storage voltage is separately provided, and the value obtained by multiplying the digital voltage value at the current time (input point of the storage circuit) by α and the digital voltage value in the storage circuit are calculated.
The sum of the digital voltage before the cycle (l is an integer of 1 or more) multiplied by β (α, β>0, α+β=1) is stored in the storage circuit.
Then, each value of the memory circuit is processed by a filter that performs Fourier integration on the grid voltage, current V, I, and positive components Vs, Is for the memory voltage Vm, which has the same phase and frequency as the grid voltage after the occurrence of a grid fault, respectively. , Mms, and residual components Vc, Ic, and Vmc are obtained and processed by an arithmetic circuit. When the following relationship is satisfied, the arithmetic circuit issues a command for the output circuit to output an on signal.

<Function> In the digital distance relay configured as above,
As mentioned above, if the memory voltage after the voltage V becomes zero due to a system fault is Vm, then ZsI−V and Vm
We are trying to determine whether the angle formed by I am trying to satisfy you.

Generally, for the inner product of complex quantities, <XY>=Re(X.) (where Re is the real part and - indicates the conjugate quantity) holds true. Therefore, if we set Zs=r+jx I=Ic+jJs V=Vc+jVs Vm=Vmc+jVms (however, s in the suffix indicates the positive component and c indicates the residual component. The same applies hereinafter), and expand the previous equation, we get VmcVc+Vms≦r( VmcIc+VmsIs) +x(VmsIc−VmcIs) (1) is obtained. According to the above formula, when V=0,
The left side is zero, but the right side is not zero, so even if a near end accident occurs, there will be no error in direction judgment. Therefore, the condition of equation (1) is determined by a filter and an arithmetic circuit.

The memory voltage Vm (i.e., Vmc, Vms) is determined by a calculation circuit by multiplying the voltage value one cycle before by β even if the grid voltage V (i.e., Vc, Vs) becomes zero due to a near-end fault in the grid. value and α of the current voltage value
Since the memory voltage is calculated by the sum of the multiplied value, the voltage is always β times the voltage value multiplied by β one cycle before, that is, the voltage gradually decreases at the same phase and frequency as the system voltage.

<Example> An example of the present invention will be described with reference to FIG.
A current transformer 2 and a voltage transformer 3 are installed in the system 1, and the current and voltage of the system 1 are transferred from these to voltage dividing circuits 4a and 4b.
Take it in. Here, isolation from system 1 is performed and at the same time it is converted to an appropriate level. Each voltage divider circuit 4
The outputs from a and 4b are analog filters 5a and 5.
b. This is a low-pass filter for removing aliasing errors. Subsequently, these outputs are given to sample and hold circuits 6a and 6b, and sampled and held in accordance with sample and hold commands sent from the control circuit 7 at regular time intervals. And each sample value is sent to multiplexer 8
sent to. The multiplexer 8 alternately sends information regarding current and voltage to the conversion circuit 9 in response to a switching command from the control circuit 7. The conversion circuit 9 converts the applied analog quantity into a digital quantity in response to a clock pulse from the control circuit 7. The converted digital instantaneous values of voltage and current are sent to the storage circuit 10, and the voltage amount is sent separately to the calculation circuit 11. The storage voltage of l cycles (l is an integer of 1 or more) before is input from the storage circuit 10 to the calculation circuit 11.
Vm is calculated. To calculate this memory voltage Vm,
As described above, the digital voltage value from the conversion circuit 9 is multiplied by α, the digital storage voltage from the storage circuit 10 one cycle before is multiplied by β, and both are added. This added value is stored in the storage circuit 10 as a digital storage voltage at that time. Memory circuit 10
stores digital values of voltage and current for one or more cycles. This series of data is sent to the digital filter 12, where it is subjected to Fourier integration to separate it into a positive component and a residual component. As a result, the above-mentioned Is, Ic, Vs, Vc, Vms, and Vmc are output regarding voltage, current, and storage voltage. This output value is given to the arithmetic circuit 13,
Here, the calculation shown in equation (1) above is executed. When the equation (1) is satisfied, the arithmetic circuit 13 issues a command to the output circuit 14 to output an on signal. In other words, this means that the accident occurred within the distance determined by the impedance Zs.

Since the storage voltage calculated by the calculation circuit 11 gradually attenuates after the occurrence of a system fault, it is necessary to lock the output circuit 14 when the peak value of the storage voltage falls below a certain level. For this purpose, the storage voltages Vmc and Vms are applied from the filter 12 to the detection circuit 15, and the peak value of the storage voltage is detected here. When the detected value falls below a certain level, an output is output and the output circuit 14 is locked.

<Effects of the Invention> As detailed above, according to the present invention, in obtaining a digital distance relay, the system voltage and current, and the voltage and current after a system fault are in phase with the voltage before the fault,
Since the memorized voltages of the same frequency are used and the distance is determined based on their positive and residual components, there is no need to provide a post-filter as in the past, simplifying the structure of the relay and eliminating the need for filters. There is no need to worry about unstable response.

In addition, the storage voltage calculation circuit stores the sum of the current digital voltage value multiplied by α and the value of β of the digital storage voltage one cycle before the current time as the storage voltage at that point in time. Therefore, even when the system voltage drops to zero due to a near-end fault, a gradually decreasing memorized voltage with the same phase and frequency as the voltage before the fault can be obtained, thereby ensuring direction error. This has the effect that it can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram for explaining the operating principle of this invention, Fig. 2 is a block diagram showing an embodiment of this invention, Fig. 3a is a block diagram showing an example of a conventional digital distance relay; FIG. 1b is a block diagram showing an example of the configuration of a conventional storage section. 1...system, 9...conversion circuit, 10...memory circuit, 1
DESCRIPTION OF SYMBOLS 1... Calculation circuit, 12... Filter, 13... Arithmetic circuit, 14... Output circuit.

Claims (1)

[Scope of Claims] 1. A storage circuit that stores digital voltage values and digital current values obtained by sampling the voltage and current of a system at regular time intervals and converting them into digital values, with one input as the digital voltage value and the digital current value; input and stored in the memory circuit (l is 1
The other input is the previous digital storage voltage value (an integer greater than or equal to a calculation circuit that outputs the sum of the values multiplied by , as a digital storage voltage at that time; and an output of the calculation circuit is used as the other input of the storage circuit to cause the storage circuit to store the digital storage voltage at that time. and performs Fourier integration on each value stored in the storage circuit to obtain the positive component Vs,
residual component Vc, positive component IS of the system current,
The residual component Ic and the positive component of the memorized voltage with the same phase and frequency as the grid voltage after the occurrence of a fault in the grid
A filter that calculates each digital value of Vms, residual component Vmc, and each component calculated by the filter is input, and VmcVc + VmsVs ≦ r (VmcIc + VmsIs) + x (VmsIc - VmcIs) (where r and x are the settling impedances) It consists of an arithmetic circuit that calculates a set value for Zs that satisfies the relationship Zs = r + jx and obtains an output signal when this is satisfied, and an output circuit that outputs an on signal based on the output signal of the arithmetic circuit. A digital distance relay characterized by: